Apple rootstock tree

ABSTRACT

This apple rootstock originated as a single seedling selected from a group of seedlings obtained from open-pollinated Malling 9 rootstock. It was chosen because of its dwarfing characteristics. It has been increased by vegetative propagation, such as stooling, and by soft- and hard-wood cuttings. Also, this clone is compatible with commercial apple cultivars.

SUMMARY OF INVENTION

The original plant of this clone came from seed of an open-pollinatedMalling 9 (Malus domestica Boskh) apple rootstock produced andpropagated by Robert F. Carlson, Department of Horticulture, MichiganState University. The seeds were collected October 1958. Afterstratification and germination, the seedlings were planted in the springof 1959, and evaluated for growth propensities that summer and fall.Several plants were selected and one of these designated as MAC-9(MAC=Michigan Apple Clone) was increased by vegetative propagation andused as a rootstock for several cultivars for further testing. MAC-9 wasselected mainly for its good dwarfing, precocity, stooling andcompatibility characteristics. This rootstock (MAC-9) will be named"Mark".

GENERAL AND DETAILED DESCRIPTION

Since MAC-9 is a clone intended to be used only as a rootstock for applecultivars, the main detailed description will center on the vegetativeparts rather than the flowers and fruits. However, the fruit will bedescribed briefly as another distinctive characteristic. It will bepropagated asexually, rather than by seed, in order to maintain clonecharacteristics.

FIG. 1 shows one year old shoots of MAC-9 from which leaves have beenremoved to show the pubescence (tomentose), the node and internodeconfiguration, the latent buds and the shoulder (bumps) below the leafscar.

FIG. 2 shows one season's growth of a stem showing tomentosecharacteristics over the bark and on the bud above the V-shaped budscar.

FIG. 3 shows root (stem) showing lenticels, their size and arrangementon the bark surface.

FIG. 4 shows typical leaves of MAC-9 showing the acute serrated marginsat sides and more obtuse serrations at the leaf base. The long, slenderpetiole is slightly grooved, with inconspicuous stipules at the base.

FIG. 5 shows top view of a growing shoot showing typical leaves arrangedin phyllotaxical order.

FIG. 6 shows a young shoot from the stoolbed showing the straight stemwith slightly cupped leaves and slender petioles.

FIG. 7 shows (left) side view of lateral bud above leaf scar, and(right) apical bud at bud break showing the tomentose characteristics.

FIG. 8 shows roots of MAC-9 formed in the stoolbed showing typical rootgrowth desirable for rapid propagation of a clone.

FIG. 9 shows shoots removed from the stoolbed showing roots originatingfrom the nodes.

FIG. 10 shows typical growth of MAC-9 in the stoolbed showing the slightoutward growth habit of the shoots.

FIG. 11 shows fruit of MAC-9 in longitudinal and cross-section showingthe closed calyx cavity and seeds. Fruit red with slight streaking,round to slightly oblong.

FIG. 12 shows (left) nine year old "Red Prince Delicious" on MAC-9, and(right) same cultivar and same age tree on MAC-5, another vigorousexperimental rootstock.

FIG. 13 shows the early bearing characteristics of trees using the MAC-9rootstock in the second season after the graft union has been made, thefirst season in the field for the complete tree.

FIG. 14 shows a mature MAC-9 rootstock in September.

DESCRIPTION OF VEGETATIVE CHARACTERISTICS

Vegetative shoots: One-year shoots are quite tomentose (fine shorthairs); bark gray-brown; lenticels widely spaced, small, inconspicuous,and yellow-white (FIGS. 1, 2 and 3).

Leaves: Leaves are of average size for apple, averaging 5 cm wide by 7cm long with uniform saw-tooth serrated margins at the sides and moreobtuse margins at the base (FIG. 4). The leaf blade tends to beasymmetric, wavy rather than flat. Leaves are in the normalphyllotaxical (3/8) arrangement for the genera (FIG. 5).

Leaf scars: The leaf scars are slightly raised above the stem and form awide V. They are deep brown (FIG. 2).

Petioles (leaf stem): These are slender, long (average 3 cm), slightlychanneled or grooved on top, and light reddish brown (FIG. 6).

Stipules (leaf-like structures at base of petiole): These are small andinconspicuous, varying from 3 to 5 mm in length, minutely serrated (FIG.4).

Buds: The dormant buds are small, angular, deep-seated immediately abovethe leaf scar, with fine white hairs (tomentose) around the bud and theleaf scar. The apical bud is obtuse, larger than the lateral buds, andconspicuously tomentose (FIG. 7).

Dormant Plant Characteristics

Shoots: Stocky, with caliper of one-year old shoots ranging from 5 to 8mm. Bark is brown to reddish and conspicuously pubescent. The stem(parenchyma and xylem) is rather resilient as compared to M. 9 which isvery brittle and breaks easily when bent.

Nodes: Nodes slightly larger in diameter than internodes, with slightshoulder (raised bumps) below and at each side of the leaf scar (FIG.1).

Internodes: Regularly spaced buds about 25 mm apart on the straightshoot (FIG. 6).

Stooling and Root Characteristics

Stooling: MAC-9 reproduces well in stoolbeds, forming strong roots withmany sublaterals (FIGS. 8 and 9). Roots form and grow on the moundedshoots during August and through December. Shoots arising from the"stool-crowns" grow slightly outward, but not as much as Malling 9, andproduction of rooted shoots is similar to that of M. 7 and MM 111. Rootsarise mostly at the nodes (FIG. 10).

Flower and Fruit Characteristics

Flowers: Smaller than average for apple cultivars, white with faintreddish streaks toward the base of the petals.

Fruit: Round to slightly oblong, red with lighter stripes, about 4 cm indiameter and 5 cm in length; tasteless and of no commercial value, butuseful for identification purposes (FIG. 11).

General Characteristics

Tree size: Size of trees budded on MAC-9 rootstock will vary somewhatwith the vigor of the cultivar and condition of soil and orchardmanagement. Standard "Delicious" is reduced in size about 50% comparedto seedling rootstock (FIG. 12). The less vigorous varieties, such as"Jonathan" are more reduced in size when budded on MAC-9.

Dwarfing: MAC-9 rootstock is dwarfing to semi-dwarfing with most applecultivars.

Precocity: Trees on this rootstock often flower and set fruit the firstyear in the field for the finished tree (FIG. 13), and tend to bearevery year.

Mature tree: The mature MAC-9 tree is dwarfed (FIG. 14). The bark colorand smoothness is characteristic. The apple cultivars are budded on therootstock from the stoolbed and thus the mature plant is not usuallyseen.

The descriptions here given of MAC-9 rootstock may vary slightly whengrown under climatic conditions different from those prevailing inMichigan.

I claim:
 1. A new and distinct variety of apple tree referred to by thecultivar name MAC-9 and substantially as herein shown and describedcharacterized particularly by its improved ability to serve as arootstock for grafting of apple tree cultivars to produce dwarf orsemi-dwarf apple trees which are early bearing, have a strong graft andhave a well anchored root system without root shoots.